Anatomically induced changes in rice leaf mesophyll conductance explain the variation in photosynthetic nitrogen use efficiency under contrasting nitrogen supply

BACKGROUND: The ratio of CO(2) mesophyll conductance (g(m)) to Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) content has been suggested to positively affect photosynthetic nitrogen use efficiency (PNUE). The anatomical basis of g(m) has been quantified, but information on the relationship between cell-level anatomies and PNUE is less advanced. Here, hydroponic experiments were conducted in rice plants supplied with ammonium (NH(4)(+)) and nitrate (NO(3)(−)) under three N levels (low, 0.71 mM; intermediate, 2.86 mM; high, 7.14 mM) to investigate the gas exchange parameters, leaf anatomical structure and PNUE. RESULTS: The results showed a lower PNUE in plants supplied with high nitrogen and NH(4)(+), which was positively correlated with the g(m)/Rubisco ratio. A one-dimensional within-leaf model revealed that the resistance to CO(2) diffusion in the liquid phase (r(liq)) dominated the overall mesophyll resistance (r(m)), in which CO(2) transfer resistance in the cell wall, cytoplasm and stroma were significantly affected by nitrogen supply. The chloroplast surface area exposed to intercellular space (S(c)) per Rubisco rather than the g(m)/S(c) ratio was positively correlated with PNUE and was thus considered a key component influencing PNUE. CONCLUSION: In conclusion, our study emphasized that S(c) was the most important anatomical trait in coordinating g(m) and PNUE with contrasting N supply. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12870-020-02731-7.